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Java > Open Source Codes > Jt > JtObservable


1
2
3 package Jt;
4 import java.util.*;
5 import java.lang.reflect.*;
6 import java.beans.*;
7 import java.io.*;
8
9 /**
10  * Jt implementation of the Observer pattern.
11  */
12
13 public class JtObservable extends JtComposite {
14
15
16   public JtObservable () {
17   }
18
19
20   /**
21     * Process object messages.
22     * <ul>
23     * <li>JtADD_OBSERVER - Adds an observer (msgContent)
24     * <li>JtREMOVE_OBSERVER - Removes an observer (msgContent)
25     * <li>JtNOTIFY_OBSERVERS - Notifies/Updates its observers when the object changes
26     * state. A JtNOTIFY_OBSERVER message is sent to the observers. A reference
27     * to this object is part of the message.
28     * </ul>
29     */
30
31   public Object JavaDoc processMessage (Object JavaDoc event) {
32
33    String JavaDoc msgid = null;
34    JtMessage e = (JtMessage) event;
35    Object JavaDoc content;
36    Object JavaDoc data;
37    JtMessage tmp, tmp1;
38
39      if (e == null)
40     return null;
41
42      msgid = (String JavaDoc) e.getMsgId ();
43
44      if (msgid == null)
45     return null;
46
47      content = e.getMsgContent();
48      //data = e.getMsgData ();
49
50
51      if (msgid.equals ("JtADD_OBSERVER")) {
52        tmp = new JtMessage ("JtADD_CHILD");
53        tmp.setMsgData (content);
54        tmp.setMsgContent (content);
55        return (super.processMessage (tmp));
56      }
57
58      if (msgid.equals ("JtREMOVE_OBSERVER")) {
59        tmp = new JtMessage ("JtREMOVE_CHILD");
60        tmp.setMsgData (content);
61        tmp.setMsgContent (content);
62        return (super.processMessage (tmp));
63      }
64
65
66      if (msgid.equals ("JtNOTIFY_OBSERVERS")) {
67        tmp = new JtMessage ("JtBROADCAST");
68        
69        tmp1 = new JtMessage ("JtNOTIFY_OBSERVER");
70        tmp1.setMsgContent (this);
71        tmp.setMsgContent (tmp1);
72        return (super.processMessage (tmp));
73      }
74
75
76      if (msgid.equals ("JtREMOVE")) {
77        return (null);
78      }
79
80
81      handleError ("JtObserver.processMessage: invalid message id:" + msgid);
82      return (null);
83
84   }
85
86  
87   /**
88    * Unit tests the messages processed by JtObserver
89    */
90
91   public static void main(String JavaDoc[] args) {
92
93     JtFactory main = new JtFactory ();
94     JtObservable observable;
95     JtMessage msg;
96     JtEcho echo1, echo2;
97     
98
99     // Create JtObservable instance
100
101     observable = (JtObservable) main.createObject ("Jt.JtObservable", "observable");
102     echo1 = (JtEcho) main.createObject ("Jt.JtEcho", "echo1");
103     echo2 = (JtEcho) main.createObject ("Jt.JtEcho", "echo2");
104
105     System.out.println ("JtObservable(JtADD_OBSERVER): adding an observer ...");
106
107     msg = new JtMessage ("JtADD_OBSERVER");
108     msg.setMsgContent (echo1);
109
110     main.sendMessage (observable, msg);
111
112
113     System.out.println ("JtObservable(JtADD_OBSERVER): adding an observer ...");
114
115     msg = new JtMessage ("JtADD_OBSERVER");
116     msg.setMsgContent (echo2);
117
118     main.sendMessage (observable, msg);
119
120     System.out.println ("JtObservable(JtNOTIFY_OBSERVERS): notifying observers ...");
121
122     msg = new JtMessage ("JtNOTIFY_OBSERVERS");
123     main.sendMessage (observable, msg);
124     
125
126     main.removeObject (observable);
127
128
129   }
130
131 }
132
133
134
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